What is happening?
Earth is changing because of global warming, which is a global average temperature increase over preindustrial times (1850–1900). As of 2020, the increase is around 1.3°C.
To appreciate how uncommon this is it is worth zooming out to the last 2000 years:
Over the last 2000 years the temperature stayed within a very narrow range of -0.5°C to +0.5°C. In fact, during the last million years Earth temperature never increased above 2–3°C over the preindustrial levels. 
How significant is a 1.3°C increase?
As a perspective, during the peak of the most recent Ice Age the planet was only about 5°C colder than today.  So each degree matters.
Especially, when you look beyond averages. For example, while Earth as a whole heated by 1.3°C, the planet’s surface temperature grew by almost 2 °C.
And some areas of surface registered temperature increases of up to 7°C.
What are the current consequences?
As the temperature increases, the ice caps are melting and the sea level rises.
It is estimated that around 600 million people live at sea level . As the sea level raises lives of these groups will become upended.
Rising seas also place coastal freshwater supplies and agriculture at risk, as saltwater moves inland, polluting rivers and aquifers, and salting the earth. 
At the same time, the surface temperature increases affect agriculture and reduce the supply of freshwater.
As we look not the future, different scenarios lead to temperature increase from 1.5°C to 4.3°C above the preindustrial level by 2100 (more on it below). The upper bound of this range means the earth will become hotter than it ever was over the last million years. It will lead to ~7°C increase in the average surface temperature and double-digit increases in some areas of the world (10°C+). As well as sea level increase of several meters.
Why is it happening?
While there are several different factors responsible for earth heating up before — orbit change and axis position, neither of these factors seem to play a role today .
Another usual suspect — solar radiation levels seems not to be involved as well, since while fluctuating the sun’s energy level stays in a quite narrow band.
What is growing — is Greenhouse gases (GHG) concentration in the atmosphere. Since there are several GHG (CO2 being the biggest contributor, but also methane, and a few others) it is helpful to look at them combined in a CO2 equivalent. On that measure, the GHG concentration increased since 1700 by around 80%.
Zooming out it looks like over the last 800,000 years earth’s atmosphere never had as much CO2 as there is now.
And what is the source of all this CO2 and other GHG? It is mostly human activity.
Starting from nineteenth century we binged on fossil fuels that powered our exponential growth from left to right.
Our energy consumption grew 30 times driven mostly by coal, oil, and natural gas. The population grew 8 times and the world GDP increased 100 times. Almost 80% of the energy we use today to support our living standards comes from fossil fuels. Look at the right picture above — almost everything on it has been created with them. Electricity that powers the lights. Asphalt, cement, steel in roads and buildings. Fuels for cars. Even apparel.
It is important to recognize that without fossil fuels this transformation would likely be impossible. But it also had unintended consequences, including saturating our atmosphere with the GHGs.
The situation today would have been much worse, if not for two counterbalancing factors: carbon sinks and aerosol masking.
Over the years we have emitted around 2500 Gt CO2. Only about 1000 Gt ended up in the atmosphere. The rest has been absorbed by the land and oceans (including plants via photosynthesis). Good for us as long as it works, but definitely has its limitations.
Aerosols are tiny particles in the air that can be produced when we burn different types of fossil fuels. When spread in the atmosphere these particles reflect the sun’s radiation back into space and thus reduce the amount of energy that reaches the earth’s surface. It is estimated that this effect masks about ~50% of global warming. In other words, the earth temperature increase would have been twice as high if not for the aerosols .
However, aerosols are bad for humans, as they pollute the air, change precipitation patterns and destroy the ozone layer. And as we transition off fossil fuels we will emit less of them anyway, reducing the masking effect, as aerosols don’t hold in the atmosphere for long (just a few days).
Where is it all headed?
Based on several scenarios, depending on how much GHG we emit from now on the estimates give temperature increase from 1.5°C to 4.3°C.
The upper bound of this range means the earth will become hotter than it ever was over the last million years. It will lead to ~7°C increase of the average surface temperature and double-digit increases in some areas of the world (>10°C), potentially leading to some areas near the equator becoming too hot to live.
Sea level depending on the scenario is projected to increase up to several meters submersing whole island-based states, like Maldives , and displacing hundreds of millions of people.
How to counter climate change?
To summarize, the earth’s temperature is increasing due to the growing concentration of GHGs in the atmosphere.
To stop global warming we must rapidly and dramatically reduce our emissions of GHG, eventually getting to zero or even to net negative (capture of the GHG from the atmosphere).
The sources of the GHGs are summarized in the table below:
- Making things (cement, steel, plastic) — 31%
- Plugging in (electricity) — 27%
- Growing things (plants, animals) — 19%
- Getting around (cars, trucks, planes, cargo ships) — 16%
- Keeping warm and cool (heating, warming, refrigeration) — 7%
Source: How to avoid a climate disaster by Bill Gates https://www.gatesnotes.com/Energy/My-new-climate-book-is-finally-here
We have technologies for some of the areas above, like heating, cooling and refrigeration, electricity generation, and passenger vehicles (electric cars).
However, inventions in other areas, like making things, growing things, and powering planes/ships are still needed.
Overall it is about 50/50 in terms of technologies we have/still need to get to net zero.
And even for the technologies that we do have, like green electricity, the amount of work is massive as we essentially need to double our generation capacity  while moving it off fossil fuels (that currently represent about 2/3 of world electricity generation ) to wind and solar (about 1/10 of the current generation), or 17x increase assuming hydro and nuclear doesn’t change significantly.
Take 2020. We had the largest capacity additions ever for solar and wind combined at 230 GW, and 280 GW if we include other renewables . However, based on the net zero scenario calculated by IEA , we will need to build out about 24 TW of capacity to fully cover the world’s needs. At the current pace, it would have taken us about 86 years.
Are we on track as humanity to limit global warming?
No, We are not.
To be on track is to reduce our GHG emissions rapidly enough to stay below 2°C global temperature increase and preferably within 1.5°C (as defined by the Paris Agreement ). These levels were agreed in 2015 because of understanding that the increase beyond 2°C will result in quicker and more unpredictable climate response, and even irreversible and disastrous consequences . And although there is no hard scientific reason to focus on 2°C (1°C or 0.5°C would have been better targets — the less the better here) this level has been established over decades of international cooperation.
However, according to the 2021 UN report, we are currently on track to reach 2.7°C by the end of the century.
After calculating all national contributions by the UN members, the authors report that the current pledges only take 7.5% off predicted 2030 emissions, while reductions of 30% are needed to stay on the least-cost pathway for 2°C and 55% for 1.5°C .
As a reminder, +2.7°C global warming means the average surface temperature increase of 4°C (oceans heat much slower), and some areas of land will heat above 10°C. The sea level will rise by about 1 m by 2100 submerging large coastal areas and island nations (to visualize see ) and displacing 10s to 100s of millions of people. Extreme weather events will increase dramatically all over the world.
Why don’t countries just reduce GHG emissions faster?
In our modern economy, we emit GHGs (either directly or indirectly) when we produce almost anything. A new TV, a parcel delivery, a hamburger, and so on. To reduce GHG emissions, a country either need to produce less or to switch to a GHG-free technology. No politician will commit their country to the former, since it means slower growth (or even decline of the GDP) and they don’t have enough certainty in green technologies to commit to faster adoption.
The good news is that if the green technologies mature faster than the politicians currently expect, the GHG emission reductions will happen faster too.
What to do about it?
So we are not on track and by a large margin due to a much slower than needed reduction in GHG. As discussed above, there are several lines of action, all important.
- Personal consumption. Switching to electricity from fossil fuels for heating and cooking, replacing ICE-cars with electric vehicles, relying more on a seasonal plant-based diet, and generally consuming less (including living in smaller homes and driving smaller cars)
- Invention and building. As mentioned above we need to invent a lot of technologies and build out already existing at an aggressive pace. We need Entrepreneurs working in this field for many decades to make it happen.
- Engaging politicians. Even when new technology becomes competitive with the existing one its implementation is often delayed by multiple factors, like significant investments made in previous generations, lack of established credibility of the new product, and overall human inertia. To achieve rapid adoption new technologies need policy support that will help overcome those factors. The invention of new technologies can benefit from effective policies too. Politicians (at least in democracies but to some degree everywhere) listen to the population and react to people’s opinions.
- Spreading the word. It is critical that every person on the planet understands the basics of Climate change.
We will have to invent and build our way out of this situation while transitioning to a more sustainable lifestyle.
The task in front of us is enormous, but there is no way around it.